Field of the Invention
The present invention relates making striae-free multicomponent chalcogenide glasses with uniform refractive index.
Description of the Prior Art
Chalcogenide glasses comprise at least one chalcogen element (S, Se or Te) and other elements including, but not limited to, Ge, As, Ga, Sn, Sb and transmit infrared light (IR) from between about 1 μm to about 12 μm or greater, depending on composition. The infrared transmitting chalcogenide glasses and optical fibers encompass the IR region of interest with numerous applications including thermal imaging, temperature monitoring, and medical applications. Also, chalcogenide glass fibers may be developed for IR missile warning systems and laser threat warning systems to provide superior aircraft survivability, and high energy IR power delivery using for example, but not limited to, CO (5.4 μm) and CO2 (10.6 μm) lasers (Sanghera et al., “IR fiber optics development at the Naval Research Laboratory,” SPIE, 3950, 180-185 (2000) and Sanghera et al., “Applications of Chalcogenide Glass Optical Fibers at NRL,” J. Optoelectronics and Advanced Materials 3 (3), 627-460 (2001)). In addition, these fibers may be developed for remote fiber optic chemical sensor systems for military facility clean-up and other industrial applications. High quality infrared transmitting optical fibers enable applications in remote chemical sensors to detect contaminants in groundwater, environmental pollution monitoring, Raman amplifiers, optical ultra-fast switches for telecommunications, fiber sources in the infrared for sensors, biomedical surgery and tissue diagnostics, and other civil/industrial process monitoring applications. Chalcogenide glasses may also be used as bulk optical elements, including windows, lenses, prisms, beam splitters and the like, and must have high compositional uniformity and homogeneity in order to maintain accurate control of light rays passing through the glass and to achieve satisfactory optical results.
Chalcogenide glasses based on arsenic and sulfur may be developed for use in many defense applications including high energy IR laser power delivery for infrared countermeasures and chemical sensors for facility clean up. The properties of the chalcogenide-based glasses, including optical, physical and thermal properties, such as refractive index, dispersion, thermo-optic coefficient, glass transition temperature, viscosity profile, hardness, fracture toughness, thermal expansion, density, nonlinear index, fluorescence and others, can be tailored through composition. However, some chalcogenide glass compositions with technologically useful properties may be thermodynamically unstable whereby crystallites or other inhomogeneities, including phase-separated glassy regions or devitrified regions, form within the glass during synthesis, melting or processing. When synthesized using the methods of prior art, this thermodynamic instability limits the physical size of the glass that may be fabricated (such as Ge30As22Se23Te25), and in some cases optical quality glass may not be made in any size due to crystal formation (such as Ge13As32Se25Te30) (Kokorina, Glasses for Infrared Optics, CRC Press, Inc. (1996)). It is well-known in the art of glass making that thermodynamically unstable glasses can be synthesized by rapidly cooling the melt, but the glasses are not optical quality due to striations that form upon rapid cooling.
The prior art methods to synthesize a chalcogenide glass from a melt are demonstrated here by example.